The present invention relates to a process for the reduction of iron-containing chrome ores in which a mixture of chrome ore, coal and slag producers, having an ore-coal ration of 1:0.4 to 1:2, and in which the slag producers CaO, MgO, Al.sub.2 O.sub.3 and SiO.sub.2 are present in such amounts that in the slag there is a (CaO+MgO)/(Al.sub.2 O.sub.3 +SiO.sub.2) ratio of 1:1.4 to 1:10 and a Al.sub.2 O.sub.3 /SiO.sub.2 ratio of 1:05 to 1:5, is heated in a rotary furnace in a CO containing atmosphere for 30 to 90 minutes at a temperature of between 1100.degree. and 1250.degree. C., then for 30 to 90 minutes at a temperature of between 1400.degree. and 1480.degree. C., and finally for 20 to 240 minutes at a temperature of between 1480.degree. and 1580.degree. C.
In DE-PS No. 34 31 854, and corresponding U.S. patent application Ser. No. 06/684,322, filed on Dec. 20, 1984, now U.S. Pat. No. 4,629,506 and assigned to the same assignee as the present application, a process for the production of ferrochromium with a carbon content of 0.02 to 10% from iron-containing chrome ores is proposed, in which a mixture of chrome ores, solid carbon-containing fuels and slag producers are heated in a rotating furnace and in which the reaction product which is taken from the rotating furnace and cooled down is melted, whereby the ferrochromium is obtained. In this process, the reduction step functions in such a manner that a mixture of chrome ore, coal and slag producers, which has an ore-coal ratio of 1:0.4 to 1:2 and in which the slag producers CaO, MgO, Al.sub.2 O.sub.3 and SiO.sub.2 are present in such amounts that the slag contains a (CaO+MgO)/Al.sub.2 O.sub.3 +SiO.sub.2) ratio of 1:1.4 to 1:10 and a Al.sub.2 O.sub.3 /SiO.sub.2 ratio of 1:0.5 to 1:5, is heated in a rotating furnace in a CO-containing atmosphere for 30 to 90 minutes at a temperature of between 1100.degree. and 1250.degree. C., then for 30 to 90 minutes at a temperature between 1400.degree. and 1480.degree. C. and finally for 20 to 240 minutes at a temperature of between 1480.degree. and 1580.degree. C.
Although in the above reduction process a reduction level of more than 95% can be attained, it has been shown that the reduction level of the reaction product varies in a disadvantageous manner. These undesirable quality fluctuations were observed particularly in large-size rotating furnaces. In addition, the above reduction process has the disadvantage that the volatile components present in the coal escape from the rotating furnace in part unused when the rotating furnace is operated in a counter flow manner. In the contercurrent flow operation, the rotary furnace is heated with burner gases which are fed into one end of the furnace in a countercurrent flow to the raw material mixture which is fed into the furnace from the other end where gas discharge devices are arranged. Since in the counter flow operation the coal is contained in the raw material mixture which is fed into the rotating furnace from the side on which the gas discharge devices are also arranged, a part of the volatile coal components leaves the rotating furnace together with the furnace waste gases because the volatile components are driven out of the coal starting as soon as the raw material mixture is fed into the rotating furnace. Thus, because of the poor use of the volatile coal components, there is a disadvantageous increase in the use of coal.